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Thread: Xflow 1700 - 185.8hp - Help with “fine” tunnig

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    Spanner Monkey jcccruz's Avatar

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    Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Hi I have a Ford Anglia with a 1700 xflow full race engine that I’ll race this seson in the Portuguese Championship.

    After some tests on the track the car has a “dip” in the mid range that is very noticible it simple wont progress until you nurse the trothle...

    This is what the dyno graph when it was build looks like - 187.7hp at 7300rpm:

    Click image for larger version Name:	E4F3D58C-6070-44D8-B108-6B1A0F424CB2.jpeg Views:	236 Size:	187.6 KB ID:	83494

    This is the car on the dyno:

    <span style="-webkit-tap-highlight-color: rgba(0, 0, 0, 0);">

    And the graph of the dyno - 185.8hp and 192nm:

    Click image for larger version Name:	73B2ADB2-2A65-4EFD-8E6A-C7657E74BB64.jpeg Views:	237 Size:	197.6 KB ID:	83495

    This was with Weber 50 DCO
    46 Venturi/Choke
    190 Main jet
    F7 Emulsion tube
    170 Air jet
    60F8 Idle jet
    100 Pump exaust valve
    45 Pump jet
    2.50 Needle valve

    The engine was too rich all the way but when we take fuel or add air the engine loose power.

    At this stage we thought the only solucion was to reduce the venturis/chokes to 42mm so we try with Weber 48ˋs with 42mm venturis we also reduce the idle jet to 50F8 and the configuration that was best was this:

    42 Venturi/Choke
    190 Main jet
    F7 Emulsion tube
    170 Air jet
    50F8 Idle jet
    100 Pump exaust valve
    45 Pump jet
    2.50 Needle valve

    Click image for larger version Name:	1C40EF86-058A-46EC-9168-E91205E5EF8B.jpeg Views:	235 Size:	191.4 KB ID:	83496

    We try to reduce the main jet and increase the air but with the same results in the middle and worst at the top...

    The engine is still too rich all the way but what puzzle me is the middle that is worst than before with the 46mm ventures???

    Any advice on the jetting this engine?

    Regards
    JC






    Last edited by jcccruz; 16-01-2019 at 11:58.

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    its not a jetting issue, its typical of a full race cam in a small high reving engine, you probably wont jet it out.

    id lay odds if you went full engine management you could improve it, but it would still be there

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Hello,

    looking at the numbers, 185 (or 182) bhp from 1700 cc is very very good, maybe too good.
    When I look at the bhp at the wheel (142) this is more like it. 43 bhp loss through the drivetrain is also too high.
    If you change from 50's to 48's and go from 46 mm chokes to 42 and almost loose no bhp that's an indication the venturi-size is too big.
    Like Graham said, a full race cam in a 1700cc Kent will not give smooth power all over the rev-range.
    You could play a bit with ignitiontiming and emulsiontubes.
    The biggest issue I see is (in my opinion / experience) the side exit exhaust; especially in the midrange this could lead to a mixture which is not good in your case way too rich.
    Regards, Leon.

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    Spanner Monkey jcccruz's Avatar

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Quote Originally Posted by Graham View Post
    its not a jetting issue, its typical of a full race cam in a small high reving engine, you probably wont jet it out.

    id lay odds if you went full engine management you could improve it, but it would still be there
    Thank you Graham

    Can you make sense why the engine his worst with 42mm chokes on the mid range for me it don’t make sense???

    With the 50 dco we have this labda values:

    Click image for larger version Name:	3BDEBE03-B74B-4432-8607-2F8B89F13F50.jpeg Views:	237 Size:	233.2 KB ID:	83498


    And with the 48 dco this with better lambda values (still rich but better) and worst power and torque:

    Click image for larger version Name:	2F63B818-3505-448C-A75E-C37161E48B83.jpeg Views:	231 Size:	233.5 KB ID:	83497

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    Spanner Monkey jcccruz's Avatar

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Quote Originally Posted by Miniliteman View Post
    Hello,

    looking at the numbers, 185 (or 182) bhp from 1700 cc is very very good, maybe too good.
    When I look at the bhp at the wheel (142) this is more like it. 43 bhp loss through the drivetrain is also too high.
    If you change from 50's to 48's and go from 46 mm chokes to 42 and almost loose no bhp that's an indication the venturi-size is too big.
    Like Graham said, a full race cam in a 1700cc Kent will not give smooth power all over the rev-range.
    You could play a bit with ignitiontiming and emulsiontubes.
    The biggest issue I see is (in my opinion / experience) the side exit exhaust; especially in the midrange this could lead to a mixture which is not good in your case way too rich.
    Regards, Leon.
    Hi Leon

    The engine was engine dyno at 187.7 at 7300 by Toovey so it’s consistent with what we see in the car dyno...

    The torque also seems right on engine dyno 139.8 lbs ft = 189.5 nm on the car dyno 192nm.

    I use this dyno a lot and I think it measure right but in this case the problem isn’t the absolute power but the 2 values between the 48’s and 50’s.

    I agree with you that seems like the 42 venturis are better in theory but my problem is in the mid range where I hope it was better even if it lost a little at the top end... but in this case it lost power everywhere...

    I hope it makes sense...

    Regards
    JC
    Last edited by jcccruz; 16-01-2019 at 13:18.

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Obviously horrible hole in the torque curve and crashing lambda ! Torque is airflow and i'd guess yours is pretty much stalled and so whatever fuel present hasn't enough air to burn it. Unless you are max WOT everywhere, i'd suspect hugely over-carb'd - would have thought 45's would work with choked down 48's as a top set up? Or as Graham says, fit EFI that will get the correct fueling & spark whatever induction and cams are fitted.

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Quote Originally Posted by katana View Post
    Obviously horrible hole in the torque curve and crashing lambda ! Torque is airflow and i'd guess yours is pretty much stalled and so whatever fuel present hasn't enough air to burn it. Unless you are max WOT everywhere, i'd suspect hugely over-carb'd - would have thought 45's would work with choked down 48's as a top set up? Or as Graham says, fit EFI that will get the correct fueling & spark whatever induction and cams are fitted.

    Hi no EFI in Classic Racing so that isn’t a option...

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Quote Originally Posted by RWD fords rule View Post
    ...
    Jason any thoughts on this???

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    What a bizarre torque curve ..
    You will allways have a dip, depending on what cam you use. But your curve has lots of dips.
    I also have 1 dip, but the size of it was surieusly decreased by changing the ignition timing.
    See my dyno, 5 years ago.



    What head and valve sizes do you use to get these great numbers?

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    You're over carbed and over choked. 48 webers (even 45s) with 38 chokes would be the max necessary for a 1700,especially with peak power at 7300rpm. You will maybe sacrifice a bit of topend power but gain a more torquey drivable engine. IMO.

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Can you give more information about the engine specs, valve sizes, CR, camshaft etc ?

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    I agree with Graham, that sort of curve isn't uncommon with a highly strung small engine. I would suggest it is definitely an air speed/scavenging issue in that spot. EFI will improve it, but only mask the issue (fixing the symptom, not the problem).
    As engines become more "high strung" it becomes harder to tune issues like this. Bottom line is that you will need to spend countless amount of hours with pipes and intake tuning to improve the issue. I would have a talk to someone like Burns Stainless in the US in regard to a recipe for some pipes (you may be surprised with the outcome for sizing). Then from there I would look at carb and choke sizing, and inlet runner length. I would have also suggested your engine is over carbed.

    We have an alloy headed xflow similar to yours making similar power, it had a great deal of time spent on it to sort this very issue. It's very time consuming, but with the right combination it can be improved.

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    The dip is almost always related to the camshaft. More precise valve lift at TDC. Fitting way to big carbs or chokes will only make it worse. With carbs it is very important to have the cam profile spot one. It usual takes a few "grinds" to get it right. Up to a level it is still all predictable, once you go full race, you are on your own, every small details start to have a lot more influence and will all take a lot of tuning time to get it right. Reason why for example a 200 Bhp Pinto will probably cost double compared to a 195 Bhp Pinto.

    The dip is mainly a result from air back flowing out of the inlet track. When carbs are fitted you can not prevent it from taking fuel twice. The mixture will be too rich and causing an even worse situation. At this level of tuning fuel injection is a better/easier option. The second dip is more some kind of "overall" tuning problem. It's possible it can be fixed with a different exhaust, intake, ..... or just not possible to get it out without loosing at other places.

    Fact is, if you got the cam and all other tuning right, it should be possible to find an excellent overall result with carbs over a wide enough power band for racing. In other words, no need for fuel injection but for some it can make the job more easy. Programmed fuel injection can mask over "cammed" engines longer.

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    Spanner Monkey jcccruz's Avatar

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    Thank you all for your replies...

    In fact my question is more why when your reduce the chokes from 46mm (Weber 50 dco) to 42mm (Weber 48 DCO) the engine lost power all over the rpm range?

    We are going to the dyno again next week just to test diferent pump jets and need valves... I’ll try also to leaner more the idle jets...

    Regards
    JC

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    Re: Xflow 1700 - 185.8hp - Help with “fine” tunnig

    I don't know why you should need 48 or 50 DCO. This engine will make full power and probably (almost sure and not a little but you can never say before testing) better torque with 45 DCOE. Choke, I guess, 36mm (maybe 38 but almost sure 38 is to big, not needed

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